The present invention relates to a fuel filter or a fuel filtering device used in a vehicle engine or the like which also functions as a water remover or a water fuel separator.
In a conventional fuel filter used, for example, in a Diesel engine, a casing made of glass or steel is mounted underneath a bracket having a fuel inlet and a fuel outlet and a filter element is accommodated in said casing. The fuel introduced from the fuel inlet flows down a central passageway and enters the casing through a lower opening. The fuel changes in flow direction to ascend in the casing and be filtered by the filter element and sent to the engine through the fuel outlet.
In such a conventional fuel filter, a major part of the water content included in the fuel or introduced from moisture in the air may fall by gravity when the fuel flows from the opening. When the fuel is reversed in direction to flow upwardly, the remainder of the water content may attach to the surface of the filter element and accumulate to form droplets, which fall and gather in the bottom of the casing. A very small amount of water may pass through the filter element but such a small amount of water is very easily fully burned in the engine and does not affect engine efficiency. The water gathering in the bottom part of the casing may be removed at a suitable maintenance interval.
A drawback has been found in such a conventional fuel filter. Since a large amount of water may attach to the surface of the filter element and accumulate thereon when the filter is in use, the surface of the filter element applied with water gathering treatment or water repellent treatment is gradually attacked by the water over a period of time so that the life of the filter element is shortened. Furthermore as a recent requirement especially related to the exhaust gas purification, it is necessary to remove the water in the fuel to substantially zero in order to accurately maintain the measuring of the fuel amount at the fuel injection valve. From this requirement it is necessary to separate the water content in the fuel as completely as possible before reaching the filter element.
The water content accumulated in the bottom part of the casing of the fuel filter is manually removed at certain regular intervals. However, if the water removing process is forgotten, the water level may reach the lower surface of the filter element. If such a situation occurs, not only does the filtering efficiency deteriorate but a large amount of water may be sent to the engine together with the fuel. This has an especially detrimental effect if the filter element is old and the filtering function has deteriorated. This is a major cause of spoiling the engine characteristics. Furthermore, rust may be induced in the injection valve which may disturb accurate measuring of the fuel.
One object of the present invention, therefore, is to provide a fuel filter which avoids the aforementioned dangerous situation.